Flat steel product is understood in the present context to refer to steel products whose width and length are each a multiple of their thickness. An example of a flat steel product is a steel strip or steel blank.
The corrosion resistance of aluminum is influenced substantially by the covering layer of Al2O3 which forms on aluminum, and by the stability of this layer. Aluminum corrodes only in strongly acidic media or alkaline solutions. The service range for aluminum alloys is therefore typically confined to the pH range of 5-8. Exceptions exist, in this respect, in relation to concentrated oxygen-containing acids such as nitric, acetic, and phosphoric acid. Moreover, the resistance of aluminum in NH3 solutions is good to very good.
Aluminum coatings for steel products are employed primarily in the form of AlSi alloys as a protection from scaling in high-temperature applications. The objective of AlSi coating, for example, is to prevent the scaling of steel sheets in the process of hot forming. As a result of hot forming (press hardening), the coating becomes brittle and then no longer affords satisfactory corrosion prevention.
However, coatings of AlSi alloys afford only moderate corrosion protection even when they are not hot-formed.